Firefox is taking 3 minutes to load a page that other browsers (Safari, Vivaldi, Chrome Canary) load in less than 2 seconds; and at 10 minutes had only loaded half of a page that the other browsers loaded in 5 seconds. Similar results with ALL web pages. Speed test results: one came back 'normal'; the other - the speed test would never work. ¶ iMac Retina 2015, Yosemite 10.10.5. ¶ I've had similar results on Google Chrome '55' since it forced me to upgrade before Christmas. I thought the slowness was a Cable problem: Download: 0.36 instead of 50; Upload 0.01 instead of 5.0; and latency 10018 ms instead of 34 ms. But after 3 technician visits, direct eithernet wiring, changing modem 3 times & all grades of restarts & speed tests - finally realized: ALL OTHER browsers work FINE; speeds are fine with them. (Also tried some other devices off of my wireless - no speed problems elsewhere - but no one else using Firefox). I was considering Firefox to replace Google Chrome, but it's giving me same problem. There are other problems with Safari (no longer supported in Yosemite), Vivaldi - (tabs, drag & drop issues), and Chrome Canary (can't be set as 'default browser') - but not speed. Ironic - the 2 'best' browsers (latest editions) with best features - are NOT working on Yosemite 10.10.5 iMac. Any suggestions?